This invention relates generally to the pumping of fluid such as water or oil from a well or formation to a collection location, and more particularly, to a downhole production unit which is coupled to a surface controller solely through a hydraulically activated power tube.
Many different types of pumps exist for pumping fluids from a remote location such as the bottom of a water well or oil well to a collection location such as a surface mounted reservoir tank. Efficiency is difficult to achieve because the fluid formation in a well may be quite deep in the ground, requiring the pump to consume excessive energy to lift the fluid from the formation to the surface.
One prior art pump for use in the water and oil well environment is the common pump jack. A frame is mounted at the surface near the well and mounts a pivotal rocker arm. One end of the rocker arm supports the sucker rods which extend into the well to the fluid formation. Counterweights at the other end of the rocker arm balance the arm. A pumping unit is mounted at the lower end of the sucker rod in the well. A motor is then used to rock the arm about its pivotal axis, causing a reciprocating motion in the pumping unit downhole to lift fluid to the surface. While the pump jack has proven generally satisfactory for many years, it is a massive unit and can often be two or three stories high. This causes the pump jack to be expensive, inefficient, and difficult to move between wells. Also, the mechanical interconnection to the downhole unit is often subject to breakdown. Moreover, the leakage of oil from the production line and lubricants at the mechanical interconnections at pump jack wellheads tends to permanently contaminate the adjacent environment.
There are other deficiencies in the pumpjack which create disadvantages. A pumpjack suitable for a small volume well and/or a shallow well cannot be used for a medium volume well and/or a deep well, and vice-versa. Thus a whole series of different capacity/depth units must be made available. Another disadvantage is the need for straight vertical alignment of the downhole unit to avoid mechanical wear during the reciprocation cycle. Finally, there are severe problems of gas-locking when the well formation fluid has gaseous material intermixed with the formation liquids.
Some of the mechanical problems of the pumpjack structure are minimized by the hydraulic pump units which transfer power to the downhole unit through hydraulic pressure. These prior art hydraulic units are nevertheless very expensive, unusually complicated and inefficient to operate, and have still not solved the gaslock problem and require extensive maintenance. Moreover, many of these hydraulically actuated pumps do not seek to maintain the hydraulic fluid and/or the power transfer fluid separate and apart from each other or from the production fluid. Also, they often use electrical components as part of the pressure control system, and may use complicated valving systems in the downhole unit.
Also, some of the prior art pumps use a downhole spring unit for providing the production force. Such mechanical device is often subject to malfunction, breakdown and/or loss of resiliency. Moreover, the return force of a spring is not constant.
Finally, while some of the aforementioned types of prior art pumps will function to some extent under optimum conditions, they lack consistent performance when typical changes occur such as change of compressibility of the column of power transfer fluid; presence of sludge, gaseous matter and/or other non-liquid additives in the production fluid; intrusion of contaminants into the hydraulic or power transfer fluid; and fluid leakages from the hydraulic or power transfer cylinders.
In summary, most of the prior art pumping units are special purpose devices which require excessive capital expenditures to purchase and install, and work only under limited conditions with respect to ranges of production (BPD), well depths, types of fluid mixtures pumped (e.g., no sludge, no gaseous mixtures), above-ground space requirements, power consumption, removability for servicing or replacement of parts, and field maintenance versus shop maintenance.
Listed below are various prior art patents which have tried unsuccessfully to provide a surface power unit in combination with a downhole production unit which efficiently uses hydraulic pressure and/or static head pressure to transfer formation fluid from a well to a collection point at the surface, without all the mechanical downhole interconnections of a pump jack: U.S. Pat. No: 436,708 issued Sept. 16, 1880; U.S. Pat. No: 376,382 issued Jan. 10, 1888; U.S. Pat. No: 1,503,602 issued Aug. 5, 1924; U.S. Pat. No: 1,616,773 issued Feb. 8, 1927; U.S. Pat. No: 1,630,902 issued May 31, 1927; U.S. Pat. No: 1,761,081 issued June 3, 1930; U.S. Pat. No: 1,981,288 issued Nov. 20, 1934; U.S. Pat. No: 2,058,455 issued Oct. 27, 1936; U.S. Pat. No: 2,122,823 issued July 5, 1938; U.S. Pat. No: 2,127,168 issued Aug. 16, 1938; U.S. Pat. No: 2,147,924 issued Feb. 21, 1939; U.S. Pat. No: 2,220,334 issued Nov. 5, 1940; U.S. Pat. No: 2,340,943 issued Feb. 8, 1944; U.S. Pat. No: 2,362,777 issued Nov. 14, 1944; U.S. Pat. No: 2,478,410 issued Aug. 9, 1949; U.S. Pat. No: 2,555,613 issued June 5, 1951; U.S. Pat. No: 2,527,184 issued Oct. 24, 1950; U.S. Pat. No: 2,917,000 issued Dec. 15, 1959; U.S. Pat. No: 2,942,552 issued June 28, 1960; U.S. Pat. No: 3,015,280 issued Jan. 2, 1962; U.S. Pat. No: 3,030,893 issued Apr. 24, 1962; U.S. Pat. No: 3,103,175 issued Sept. 10, 1963; U.S. Pat. No: 3,123,007 issued Mar. 3, 1964; U.S. Pat. No: 3,374,746 issued Mar. 26, 1968; U.S. Pat. No: 3,804,557 issued Apr. 16, 1974; U.S. Pat. No: 3,589,838 issued June 29, 1971; U.S. Pat. No: 4,026,661 issued May 31, 1977; U.S. Pat. No: 2,490,118 issued Dec. 6, 1949; U.S. Pat. No: 4,028,013 issued June 7, 1977; U.S. Pat. No: 4,031,385 issued Mar. 22, 1977; U.S. Pat. No: 4,285,422 issued Aug. 25, 1981; U.S. Pat. No: 4,295,799 issued Oct. 20, 1981; U.S. Pat. No: 4,381,177 issued Apr. 26, 1983; U.S. Pat. No: 4,390,326 issued June 28, 1983; U.S. Pat. No: 4,403,919 issued Sept. 13, 1983; U.S. Pat. No: 4,449,892 issued May 22, 1984.
A need therefore exists for an improved pumping unit which incorporates the benefits of downhole fluid power transmission from a surface powered pump while avoiding the prior art disadvantages of complexity, size, weight, breakdowns, inefficiency, high maintenance costs, and malfunctions due to gaseous materials and other contaminants in the various fluid systems of the apparatus.
The most recent well pumping apparatus with which we are familiar and which incorporates a column of power transfer fluid located in the well casing is disclosed in Patent Application Ser. No: 662,963 filed Oct. 19, 1984, now U.S. Pat. No. 4,616,981 entitled IMPROVED PUMPING APPARATUS WITH A DOWN-HOLE SPRING LOADED PISTON ACTUATED BY FLUID PRESSURE. Nevertheless, the invention of the present application eliminates the need for a spring in the downhole unit and constitutes a substantive and unique improvement which provides efficiency, reliability, and versatility which to some extent were found to be lacking in the pumping apparatus of such previously filed application.
It is an object of the present invention to overcome the aforesaid deficiencies of the prior art pumps, and to provide an improved method and apparatus for efficiently pumping oil, water or other fluid from a well formation up to the surface, without any mechanical interconnection between the surface controller unit and the downhole production unit. A related object is to eliminate the need for any mechanical energy device like a spring in the downhole unit.
Another object of the invention is to provide an improved pump method and apparatus which employs three separate fluid systems, namely, a hydraulic fluid system for controlling the movement of a hydraulic piston, a power fluid system for transferring the pressure generated by the hydraulic piston to the downhole piston assembly, and a production fluid system for carrying the formation fluid up the well to an outlet or storage tank. A related object is to isolate the hydraulic fluid system from the power fluid system and similarly to isolate the power fluid systems from the production fluid systems during normal operation of the invention.
Still another object of the invention is to transfer production fluid up to the surface during a power stroke of the hydraulic piston. A related object is to provide a high efficiency embodiment which utilizes the static head of the production fluid column to reset the downhole piston assembly and which utilizes any additional resetting force to assist in moving the hydraulic piston through its return stroke.
Yet another object of the invention is to provide pressure sensing valves in the surface hydraulic actuator unit so that the hydraulic piston does not start its return stroke until the downhole piston assembly has completed the full length of its production stroke, to avoid incomplete production inefficiency due to compressability of the power transmission fluid.
Still a further object of the invention is to provide an alternate embodiment incorporating two power tubes each having a pulser piston respectively coupled to opposite ends of the hydraulic piston. A related object is to connect the power tubes to two or more wells to increase the efficiency of multiple well installations, or alternatively to connect both power tubes to a single well.
It is a further object of the invention to provide a relatively lightweight pumping unit which can be installed by one person, which operates quietly and efficiently at a production rate that can be easily varied, and which can be mounted at the top of a well in a low profile or underground location, and which employs standard component parts which can be easily repaired or replaced during operation over many years. A related object is to eliminate the mechanical devices which have been typically used in prior art pumps such as stuffing boxes, belts, pulleys, polish rods, springs, electric switches, and the like which have short production life expectancies and which utilize excessive energy.
Another object is to provide a pumping apparatus which allows the rate of flow from the well production tube to be increased or decreased without having to reinstall a new set of pumping equipment.
A further object is to provide a pump apparatus where the size of the surface unit does not significantly increase even though the depth and/or production volume of the well production unit is increased. A related object is to provide a full range of ratios beginning with less than two-to-one based on comparing the linear displacement of the downhole unit with the corresponding linear displacement of the pulser piston in the hydraulic actuator.
Yet another object is to provide a method of well pumping which allows the amount of the return force transmitted in the counterbalance chamber(s) of the downhole unit to be easily modified as needed for each individual well installation. A related object is to provide a priming line in the hydraulic actuator unit for supplying hydraulic fluid to the hydraulic cylinder in instances where an excess of return force in the downhole counterbalance chambers speeds up the return stroke of the hydraulic piston during the resetting mode.
A further object is to provide variations in the design of the downhole pump assembly in order to meet diverse environmental conditions, including three piston units (power piston, counterbalance piston(s), and production piston), two piston static head units (combined power/production piston, counterbalance piston), two piston dual power tube units (power piston, dual production piston), and multiple piston units (power piston, one or more single/dual production pistons.
A still further object is to eliminate electrical components so that all control valves in the hydraulic actuator are pressure activated. A related object is to minimize electrical energy consumption by having a low horespower motor for the hydraulic pump as the only electrical component in the system.
These and other objects of the invention will become evident to those skilled in the art based on the exemplary embodiments of the invention shown in the attached drawings and described in detail hereinafter.